The amended suit, filed in a New York federal court Monday, reiterated accusations that Jon S. Corzine, MF Global's former chief executive, and other officials at the commodities and securities brokerage firm breached their fiduciary duty to MF Global customers and violated the Commodity Exchange Act.

But it also added a player with deep pockets to the mix as customers continue to try to recover an estimated $1.6 billion that went missing from their accounts when MF Global filed for bankruptcy on Oct. 31, 2011.

The suit, which seeks class action status, detailed many of the same findings as a bankruptcy trustee, James Giddens, did in a June report. After that, the trustee assigned his claims against former MF Global officers to plaintiffs' law firms in an attempt to reduce the legal costs of recovering money for customers.

The latest move in the MF Global case comes as civil regulatory investigations continue. A criminal probe hasn't resulted in any charges.

Approximately 36,000 customers of MF Global's U.S. brokerage have filed claims with Mr. Giddens' office. Many of them have received about 80 cents on the dollar of cash owed to them, while customers who invested on foreign exchanges have received only about five cents, due to disputes about how the money should be treated under U.K. bankruptcy law.

"I'm optimistic we'll recover all the customer money and hopefully a good chunk of money for the general estate," said Andrew Entwistle, managing partner at Entwistle & Cappucci, one of the two firms leading the representation of MF Global's commodities customers.

The complaint alleges that PwC, as MF Global's auditor, said that the firm's internal controls for safeguarding customer assets were adequate when in fact they weren't, and that PwC should have known they weren't.

The complaint alleges that PwC breached a fiduciary duty to MF Global and its customers and was negligent in its work at the firm. "If they had made sure the internal controls were adequate, there never would have been an invasion of customer funds," said Merrill Davidoff, a managing principal at Berger & Montague, which is also representing the commodities customers.

In 2010 and 2011, according to the complaint, PwC was copied on several MF Global internal-audit reports that indicated there were deficiencies in the firm's internal controls, the complaint alleges.

In 2010, according to an internal review by MF Global cited in the complaint, there were five instances in which the firm drew on customer funds to such a degree that it was "funded by clients." That isn't necessarily against federal commodities rules, but it exposed the firms' clients to risks.

The complaint also alleges that PwC failed to adequately examine and evaluate MF Global's procedures and controls for protecting customer funds, failed to adequately test calculations for the segregation of customer funds and failed to issue going-concern warnings for MF Global when it should have.

A PwC spokeswoman declined immediate comment until the firm had time to review the complaint.

Meanwhile, J.P. Morgan Chase & Co. was taken off the case as a defendant as part of an agreement that will allow plaintiffs to review the bank's involvement with MF Global. The lawyers could put J.P. Morgan back on as a defendant later.

Several other defendants remained from the original filing. They included Mr. Corzine, a former New Jersey governor and U.S. senator and ex-chairman of Goldman Sachs Group Inc., and seven other executives of the firm.

CME Group Inc., the exchange company that both regulated MF Global and charged it fees for handling its trades, also was named as a defendant on the case. A CME spokeswoman said the firm doesn't comment on litigation, but added that "as an industry, we are focused on rebuilding confidence going forward."